A conventional navigation system having a storage device, a processing device, an input device, a display device, sensors and the like and a navigation method to be executed in the system may be classified into the following two types on the basis of the contents displayed on the display device as driving information provided for a user.
One of the two types is a map display system which is arranged in such a manner that a map is displayed on the screen of the display device and a travelling locus, a present position, a moving direction, a target, a target direction, an instructed course or the like are indicated in the map. Another one is an arrow display system which is arranged in such a manner that no map is displayed but arrows respectively showing the target direction and the course instruction at each intersection are indicated.
The map display system and the arrow display system respectively have encountered the following problems:
According to the map display system, a driver must look at the displayed map while driving a vehicle. Therefore, the driver must pay attention to many factors and thereby the driver will be exhausted, causing a load to be applied to the driver. Furthermore, a risk will arise as the case may be. Therefore, in the conventional map display system, the display device has been disposed in a lower position so that the driver cannot look at it during driving, or only main roads are indicated during driving. However, these devices could not satisfactorily overcome the problems and thereby a risk in terms of traffic safety remains. Because of the risk, the European countries have denied the map display system and therefore they have not employed the map display system.
The arrow display system encounters the following two typical problems: In a case where the target direction is shown by an arrow as one of the display modes of the display device, the driver psychologically tends to perform earlier turns to the right or left in accordance with the shown arrow, causing a problem to arise, for example, the vehicle strays in a residential area. Furthermore, in a case where the course is instructed at an intersection as another display mode, timing at which traffic information collected in real time is indicated and acceptability for the drivers, which becomes a serious problem for the aged and female drivers, remain as unsolved problems, because there is a course instruction as the assumption.
According to a basic system design concept used for developing the conventional navigation system, the most important factor for the navigation system lies in that the present position of the user's vehicle, which is moving, is accurately recognized in a map (road map) which has been previously prepared. This system design concept is similarly applied to both the map display system and the arrow display system.
However, the conventional navigation system developed in accordance with the basic system design concept has been restricted by the system design concept and thereby it is of no practical use at present.
That is, since the vehicle such as an automobile moves at considerably high speed, it is not so practical for the driver even if the driver recognizes the present position of the vehicle as a point of low accuracy on the road map displayed on the display device. That is, it is rather acceptable for the driver who is driving the vehicle, in the aspects of the speed sensibility and the sense about the positional relationship and the directional relationship with respect to his target, that the driver recognizes the state of the vehicle's movement as a line while making the positional relationship with respect to the target clear than recognizing the present position indicated as a point, on the screen of the display device. It is easier and more natural for the driver to recognize the state of the vehicle's movement as the line than to recognize the state of the movement as the point. Furthermore, information about the state of the movement as the line is more valuable as available drive information. In addition, since the user's vehicle such as an automobile must move while being restricted by a road in a different manner from an airplane and a ship, it is more practical to recognize the road on which the user's vehicle is moving at a particular moment while making the positional relationship with the target for the user's vehicle clear than obtaining the present position of the user's vehicle as a point.
Furthermore, if the present position of the user's vehicle is intended to be accurately obtained, the load of realizing the high accuracy becomes too heavy for the navigation system. As a result, the cost for manufacturing the navigation system cannot be reduced and thereby wide use of the navigation system will be interrupted. Therefore, the primary ideal of preventing the traffic snarl and realizing the safety traffic cannot be achieved.
It is very dangerous for the driver to drive his vehicle while actually looking for a road. Therefore, there has been a desire of a practical navigation system to be developed as a system of aiding the driver to easily reach the position of the target. According to the conventional navigation system arranged in accordance with the map display system, the driver must look for the driving course set on the road map displayed on the display device. Therefore, the dangerous factor cannot be eliminated and thereby its practicality is insufficient.
Since the driver must pay attention to many things during driving the vehicle, the load of the driver must be reduced for the purpose of safely driving the vehicle. Therefore, it is preferable that a navigation system be arranged in such a manner that information necessary to select the course can be obtained at first glance.
According to the conventional navigation system arranged in accordance with a route guide system in which the driving course through which the vehicle reaches the target is indicated on the display device, an optimum driving course is set in accordance with the relationship between the start position and the target position at the time of start of driving. According to the above-described navigation system arranged in accordance with the route guide system, it is actually difficult to drive the vehicle while keeping the driving course in the actual road state even if the driving course is indicated on the display device. Furthermore, the degree of the danger can be increased due to stress given to the driver when the determined driving course is instructed for the driver.
However, if the instruction by means of indicating the driving course is not made but only the present position of the user's vehicle is indicated, the value of information is insufficient. It is more dangerous to look for the course in accordance with the present position shown on the road map displayed on the display device than to instruct the driving course.
It is important for the navigation system to, via the display device, show the driver information which is valuable to reach the target in a state in which safety cannot be deteriorated. In particular, intense stress is given to the driver if the optimum driving course to reach the target is determined before the start of driving and the one fixed driving course is shown to the driver. In order to prevent the state in which the stress is given to the driver, it is preferable that the navigation system be constituted in such a manner that the driver is able to select a course to reach the target and the driver's determination about the selected course is given priority. As a result, the driver is able to drive the vehicle with composure.
Furthermore, the current background in which the aged and the female drivers increase must be taken into consideration. In addition, the mental state and recognition of the driver in a specific situation must be considered.
Therefore, it is insufficient for the display device to indicate the present position of the user's vehicle on the road map. In addition, it is an excessive function to indicate the driving course on the map.
An object of the present invention is to provide a significantly practical navigation system and a method therefor capable of overcoming the above-described problems and meeting the above-described requirements by regarding information about the movement state of a moving object as a line as important and employing a concept of a "line representing a passage through which the moving object is moving at this very moment", that is a "travelling line", whereby necessary and minimum practical information is supplied to a user such as a driver to cause the user to independently select the course.
Another object of the present invention is to provide a navigation system and a method therefor in which a novel and practical navigation display system is employed which is completely different from the conventional map display system and the arrow display system in terms of the display method and which is arranged completely different from the course guide system in terms of a navigation principle such that the driving course is not set previously but a user is able to independently make the driving course while selecting a course in accordance with the determination about driving made by the user.